1. Field of the Invention
This invention relates to integrated circuit structures. More particularly, this invention relates to a silicon oxide dielectric material with a low dielectric constant useful in the formation of a dielectric layer in an integrated circuit structure.
2. Description of the Related Art
The shrinking of integrated circuits has resulted in levels of interconnects, including metal interconnects, being placed closer together, as well as reduction of the horizontal spacing between metal lines on any particular level of such interconnects. As a result, capacitance has increased between such conductive portions, resulting in loss of speed and increased cross-talk. One proposed approach to solving this problem of high capacitance is to replace the conventional silicon oxide (SiO.sub.2) dielectric material, having a dielectric constant (k) of about 4.0, with another insulation material having a lower dielectric constant to thereby lower the capacitance.
In an article by L. Peters, entitled "Pursuing the Perfect Low-K Dielectric", published in Semiconductor International, Volume 21, No. 10, September 1998, at pages 64-74, a number of such alternate dielectric materials are disclosed and discussed. Included in these dielectric materials is a description of a low k dielectric material having a dielectric constant of about 3.0 formed using a Flowfill chemical vapor deposition (CVD) process developed by Trikon Technologies of Newport, Gwent, U.K. The process is said to react methyl silane (CH.sub.3 --SiH.sub.3) with hydrogen peroxide (H.sub.2 O.sub.2) to form monosilicic acid which condenses on a cool wafer and is converted into an amorphous methyl-doped silicon oxide which is annealed at 400.degree. C. to remove moisture. The article goes on to state that beyond methyl silane, studies show a possible k of 2.75 using dimethyl silane in the Flowfill process. The Peters article further states that in high density plasma (HDP) CVD, dielectric material formed from methyl silane or dimethyl silane and O.sub.2 can provide a k as low as 2.75; and that trimethyl silane, available from Dow-Corning, can be used to deposit low-k (2.6) dielectric films.
An article by S. McClatchie et al. entitled "Low Dielectric Constant Oxide Films Deposited Using CVD Techniques", published in the 1998 Proceedings of the Fourth International Dielectrics For ULSI Multilevel Interconnection Conference (Dumic) held on Feb. 16-17, 1998 at Santa Clara, Calif., at pages 311-318, also describes the formation of methyl-doped silicon oxide by the low-k Flowfill process of reacting methyl silane with H.sub.2 O.sub.2 to achieve a dielectric constant of .about.2.9. The authors then further describe the formation of low-k dielectric material using dimethyl silane (CH.sub.3).sub.2 --SiH.sub.2, thereby achieving a dielectric constant of .about.2.75. However, the authors point out that the methyl silane and the dimethyl silane both result in carbon being bound into the oxide lattice via a Si--CH.sub.3 bond which results in the termination of the siloxane chain. The authors further state that the addition of further CH.sub.3 groups bound to the silicon atom is thought to be prohibitive because an increase in the number of CH.sub.3 groups reduces the number of sites available to form the siloxane chain. Instead, the authors reported taking a different approach by incorporating the carbon as part of the siloxane chain itself so that the siloxane chain would not be broken. The authors then report on the use of methylenebis-silane (SiH.sub.3 --CH.sub.2 --SiH.sub.3) instead of methyl silane as the precursor material reacted with H.sub.2 O.sub.2 whereby the SiH.sub.3 functional groups can take part in the polymerization reactions with H.sub.2 O.sub.2 leaving the Si--CH.sub.2 --Si backbone intact as a part of the siloxane chain, and state that a dielectric material having a dielectric constant of .about.2.7 can be achieved by using methylenebis-silane in place of methyl silane as the precursor.
Attempts have been made to lower the dielectric constant of the film by increasing the carbon content in the dielectric film using phenyl silane as the precursor. While a film having a low dielectric constant was obtained, using a phenyl silane precursor, the dielectric constant was found to vary from film to film with k values between .about.2.1 to .about.2.8, i.e., formation of a film with a given k value was not reproducible.
It would, therefore, be desirable to reproducibly form a carbon-containing silicon oxide dielectric material having a dielectric constant preferably as low as or lower than the dielectric constant of the carbon-containing silicon oxide dielectric material formed using methyl silane as the precursor. It would also be desirable to be able to control or tailor the dielectric constant of a carbon-containing silicon oxide dielectric material formed using a carbon-containing silane precursor to achieve a particular dielectric constant without sacrificing other physical properties of the resulting carbon-containing silicon oxide dielectric material.